Kowshik Nandagudi wrote:where can i find all the class files of in built java Classes in jdk? i.e String Class, StringBuffer Class etc...

Why would you want to?
And do you mean- .class files? They would be in the lib directory in the form of jars. If you wanted the Source- they would be in the src.zip file in the JDK installation directory.

Really? I've installed many JDKs in my lifetime, but I don't remember the docs ever being part of the installation. You can download it from Oracle's Java site though, then unzip it to any folder you want.